Galactic Collision May Contain Clues About Dark Matter

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Galactic Collision May Contain Clues About Dark Matter

A newly discovered galactic smash-up may give astronomers insight into the behavior of galaxy collisions and the nature of dark matter.

The Musket Ball Cluster, located about 5.23 billion light-years from Earth in the constellation Cancer, is about 8 million light-years across. Scientists have previously seen about half a dozen such collisions, which occur when galaxy clusters – groups of galaxies gravitationally bound together – violently crash together. The textbook case is the Bullet Cluster, where one galaxy cluster is seen shooting through the other.

The Musket Ball Cluster gets its nickname because it is very similar to the Bullet Cluster, but older and slower. Researchers estimate the Musket Ball is about 700 million years into its collision, roughly two to five times farther along than the Bullet Cluster.

The violent processes in cluster collisions create huge amounts of hot gas that likely influence the evolution of the galaxies within them. But scientists don't yet know many of the details, such as whether the mergers trigger star formation, suppress it, or have no effect.

Galactic clusters also contain some of the largest accumulations of dark matter in the universe. By carefully observing the distribution of visible matter, scientists may be able to infer what happens to the dark matter during the crashes. In one bizarre case, the collision dynamics have left behind a huge lump of dark matter.

Many of the most basic questions about dark matter remain unanswered. No one yet knows if dark matter can collide with itself, though current evidence suggests dark matter particles interact little with other dark matter. Knowing the details of galaxy-collision processes may help scientists determine the characteristics of dark matter particles and narrow down the list of possible particles that could be dark matter.